The present invention generally relates to a method of encasing electric components and, more particularly, to a method for the formation of an outer protective coating in an electric component, such as a ceramic capacitor or the like, of a type having at least one pair of lead wires extending outwardly from the body of the electric component in the same direction for external electric connection.
Electric components of the type referred to above are largely employed in electric and/or electronic equipments and are generally mounted on printed circuit boards with their lead wires soldered to printed circuit wirings. One example of the electric components, for example, a ceramic capacitor, is illustrated in FIG. 1 of the accompanying drawings, with a portion broken away, in the form as mounted on a printed circuit board. Referring to FIG. 1, the prior art ceramic capacitor 8 comprises a generally disc-shaped component body 4 including a sintered dielectric plate 1 of any known dielectric material, for example, barium titanate, and a pair of electrode discs 2 and 3 attached respectively to the opposed surfaces of the dielectric plate 1, lead wires 5 and 6 equal in number to the number of the electrode discs 2 and 3, each of said lead wires 5 and 6 having one end soldered to the corresponding electrode disc 2 or 3, and an outer protective coating or casing 7.
According to the prior art, the outer protective coating 7 is formed by dipping the component body 4 into a coating solution, then drying the component body 4 after the latter has been withdrawn out of the coating solution, and finally baking the dried component body 4 to allow the layer of the coating solution to be hardened or cured.
However, the prior art encasing method involves a disadvantage. Specifically, since the protective coating 7 must cover the entire surface of the component body 4, the component body 4 is completely immersed into the coating solution in its entirety during the dipping process. The complete immersion of the component body 4 into the coating solution results in unnecessary coating of the coating solution to respective portions of the lead wires 5 and 6 adjacent to the component body 4, involving waste of the coating solution. In addition, where the drying is effected while the coated component body 4 is supported in a manner with the lead wires 5 and 6 oriented downwards, the coating solution applied not only to the component body 4 but also to that portions of the lead wires 5 and 6 adjacent the component body 4 tends to flow downwards along the lead wires 5 and 6, which solution, when dried, forms generally downwardly tapering buldges, such as shown by 9 and 10, at the respective portions of the lead wires 6 and 5 adjacent the component body 4.
In general, the buldges of the coating material so formed according to the prior art encasing method often run about 3 to 5 millimeters. Therefore, unless the buldges of the coating material are minimized or substantially eliminated, the height of the ceramic capacitor 8 relative to the printed circuit board 11 tends to become large when it is mounted on the printed circuit board 11 with the lead wires 5 and 6 soldered to the printed circuit wirings. This is because the buldges 9 and 10 themselves serve as undesirable spacer spacing the component body 4 a distance away from the printed circuit board. As is well known to those skilled in the art, the larger the space between the component body 4 and the printed circuit board 11, the more bulky the electric or electronic equipments tends to become.
In addition, in view of the fact that the buldges of the coating material in one given ceramic capacitor tend to have different lengths, difficulties are often involved in mounting the ceramic capacitor precisely on the printed circuit board.
Attempts to minimize the buldges of the coating material such as shown by 9 and 10, have not been successful because of the limitations imposed by (1) the diameter and the thickness of the dielectric plate 1, (2) the fitting angles of the lead wires 5 and 6 relative to the corresponding electrode discs 2 and 3, (3) the wettability and the viscosity of the coating solution and the depth of immersion of the component body, and (4) the skill of attendant workers.